The colouration of the venomous coral snakes (family Elapidae) and their mimics (families Aniliidae and Golubridae)

The bright coloured, highly venomous coral snakes, Leptomicrurus, Micrurus and Micruroides (family Elapidae) and a series of harmless or mildly toxic mimics form an important component of the snake fauna of the Americas. Coral snake patterns are defined as any dorsal pattern found in any species of venomous coral snake and/or any dorsal pattern containing a substantial amount of red, pink or orange distributed so as to resemble that of some species of venomous coral snake. The components of coral snake colouration are described and four principal dorsal patterns are recognized: unicolour, bicolour, tricolour and quadricolour. The tricolour patterns may be further clustered based on the number of black bands or rings separating the red ones as: monads, dyads, triads, tetrads or pentads. A detailed classification of all coral snake colour patterns is presented and each pattern is illustrated. The taxonomic distribution of these patterns is surveyed for mimics and the 56 species of highly venomous coral snakes. Among the latter, the most frequent encountered patterns are tricolour monads, tricolour triads and bicolour rings, in that order. No venomous coral snakes have a tricolour dyad, tricolour tetrad or quadricolour pattern. As many as 115 species of harmless or mildly toxic species, c. 18% of all American snakes, are regarded as coral snake mimics. The colouration and behavioural traits of venomous coral snakes combine to form a significant antipredator defence of an aposematic type. The mimics in turn receive protection from predators that innately or through learning avoid coral snake colour patterns. The precise resemblances in colouration between sympatric non-coral snakes and venomous coral snakes and the concordant geographic variation between the two strongly support this view. Batesian mimicry with the highly venomous coral snakes as the models and the other forms as the mimics is the favoured explanation for this situation. It is further concluded that a number of species in the genera Elaphe, Farancia, Nerodia and Thamnophis, although having red in their colouration, should not be included in the coral snake mimic guild.